1. Field of the Invention
The present invention relates to a method for making a vacuum airtight container. More specifically, it relates to a method for making a vacuum airtight container used in a flat panel display.
2. Description of the Related Art
In a method for making a vacuum airtight container used in a flat panel display, it is important to accurately align a front substrate and a rear substrate to each other before bonding and to perform highly airtight sealing, and these are required to be performed at low cost.
Japanese Patent Laid-Open No. 2001-229828 (corresponding to EP 1126496) discloses a low-cost bonding technique in which a front substrate and a rear substrate are bonded in a vacuum chamber using a low melting point metal as a bonding material. By using a low melting point metal as a bonding material, the time required for heating and cooling can be reduced. Therefore, the takt time can be reduced, and the bonding cost can be reduced.
Japanese Patent Laid-Open No. 11-135018 (corresponding to US 2001/0009836) discloses a technique for accurate alignment and bonding in which bonding is performed while performing alignment in a vacuum chamber. Since alignment is performed in a vacuum chamber in this technique, this technique requires a mechanism that measures the relative positions of the front substrate and the rear substrate in the vacuum chamber and corrects the positions. This increases the cost of the apparatus, and therefore a production method using a simple apparatus is desired.
Japanese Patent Laid-Open No. 2006-093117 (corresponding to US 2006/0042316) discloses a technique in which a low melting point metal is used as a bonding material, and a front substrate and a rear substrate are aligned to each other beforehand and then bonded in a vacuum chamber. According to this technique, a low melting point metal is used as a bonding material, and alignment is performed beforehand in air. Therefore, the vacuum chamber need not be provided with an alignment mechanism, and the cost can be reduced. However, from the viewpoint of airtightness, there is still room for improvement.